1/2 si 1/4 pot avea numitor comun pe 4,8,12
2/3 si 4/9 ....................................... 9,18,27
3/2 si 1/6........................................6,12,18
1/2 si 5/8.........................................8,16,24
3/10 si4/30........................................30,60,90
5/3 si 3/4............................................12,24,48
5/6 si 5/7............................................42,84,168